Level measurement technologies include ultrasound and radar typically being Guided Wave Radar (GWR). Newer level measurement devices are TDR-based that utilize sound or echo-based measurement whether ultrasound or GWR. GWR is a contact radar technique to measure the level of liquids or solids in a tank using time TDR principles.
GWR works by generating a stream of pulses of electromagnetic energy and propagating transmitted pulses down a transmission line formed into a level sensing probe. The probe is generally placed vertically in a tank or other container and the electromagnetic pulse is launched downward from the top of the probe. The probe is open to both the air and the material to be sensed in such a way that the electromagnetic fields of the propagating pulse penetrate the air until they reach the level of the material. At that point, the electromagnetic fields see the higher dielectric constant of the material. This higher dielectric constant causes a reduction in the impedance of the transmission line, resulting in a pulsed reflected (echo) signal back to the top of the probe. The pulse travels through the air dielectric portion of the probe at a known velocity. This allows the material level and an interface thickness (if present) to be determined by a peak finding algorithms that identifies peak(s) in the pulse echo curve.